grid1=[[1,0,0,0,0,0,1],[2,0,0,0,0,3,0],[2,0,9,0,0,0,0],[0,3,0,5,4,0,0],[1,0,2,3,0,0,6]]
grid2=[[3,1,1],[2,5,1],[1,5,5],[2,1,1]]
grid3=[[2,4,4],[8,5,2],[9,5,0],[2,4,1]]

